The present invention relates to a method of raising the temperature of a reducing gas containing a CO component for avoiding the troubles caused by soot inevitably generated in raising the temperature of the reducing gas.
A reducing gas having CO and H.sub.2 as its main components controlled at a particular temperature is very useful as a gaseous reducing agent for example, for iron ores. In the operation of a blast furnace, the reducing gas forced into the interior of the blast furnace effectively serves to accomplish the gas reduction of the charged ores so that the lowering of the coke ratio and the improvement in the productivity are achieved. Further, in a method of producing reduced iron other than the blast furnace process, the above described reducing gas is highly useful as a heat source for the reducing furnace and as the gaseous reducing agent. The reducing gas may also be used as an agent for heat-treatment of the reduced iron, such as, a desulfurization, carburizing, or other gaseous treating agent.
Reducing gas used as a gaseous reducing agent or heat-treating agent and having CO and H.sub.2 as its main components is obtained in the form of a high temperature reducing gas at a temperature higher than 1000.degree.C, for example, by means of the partial oxidation of a hydrocarbon fuel, steam reforming processes, etc. The high temperature reducing gas is blown into the reducing furnace with the temperature thereof being appropriately adjusted. The amount of the gas used in the reducing furnace is determined by various conditions, such as the volume of the furnace, and the desired results. In any event, large volumes are used. On the other hand, the rate of utilization of the gas in the reducing furnace is far below 100%, and therefore, unused reducing gas, containing H.sub.2 O and CO.sub.2, is discharged from the top of the reducing furnace is collected and regenerated by a gas circulating system and used again as the gaseous reducing agent. It is necessary to raise the temperature of the thus regenerated reducing gas which has cooled to a lower temperature to a higher blowing temperature needed for the reducing furnace. In the regenerating process for the reducing gas in the above described circulating system, when a catalyst is used, it is necessary to preliminarily raise the temperature of the gas to be treated to a temperature desired for the reforming process. Also, in the case of a low temperature reducing gas obtained by a production process other than that described above, the gas is required to be heated to a temperature desired for the utilization thereof.
In raising the temperature of the reducing gas for the regeneration process described above or for the using it as a gaseous reducing agent, the equilibrium will proceed toward the right in the following equation, when the reducing gas containing a CO component is indirectly heated, EQU 2 CO.revreaction. CO.sub.2 + C
thereby producing carbon (soot) from the gas and generating CO.sub.2.
The thus separated soot adheres to the heating tubes so that not only is the heat conducting efficiency lowered, but also, the flow path of the gas is blocked, thereby making it impossible to raise the temperature of the reducing gas. If the reducing gas is processed for the regeneration by using a catalyst, the separated soot adheres to the surface of the catalyst thereby significantly deteriorating the function of the catalyst. Thus, technical measures for prolonging the effective function of the catalyst or quickly changing the catalyst are required. These measures generally disturb the continuous process used to improve the quality of the gas.